Multi-mode tags and methods of making and using the same

ABSTRACT

Multi-mode (e.g., EAS and RFID) tags and methods for making and using the same are disclosed. The tag generally includes an antenna, an electronic article surveillance (EAS) function block coupled to the antenna, and one or more identification function blocks coupled to the antenna in parallel with the EAS function block. The method of reading the tag generally includes the steps of applying an electric field to the tag, detecting the tag when the electric field has a relatively low power, and detecting an identification signal from the tag when the electric field has a relatively high power. The present invention advantageously enables a single tag to be used for both inventory and anti-theft purposes, thereby improving inventory management and control at reduced system and/or “per-article” costs.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/851,122, filed Oct. 11, 2006, and U.S. Provisional Application No.60/880,827, filed Jan. 16, 2007, both of which are incorporated hereinby reference in their entireties.

FIELD OF THE INVENTION

The present invention generally relates to EAS (electronic articlesurveillance) and/or RFID (radio frequency identification) tags. Morespecifically, embodiments of the present invention pertain to multi-mode(e.g., “dual use” tags, having EAS and RFID functions thereon, forexample) tags and methods for making and using the same.

DISCUSSION OF THE BACKGROUND

As is known in the art, EAS tags are useful for anti-theft detection,but generally do not store enough information for inventory control. Onthe other hand, RFID tags typically do not have an operational rangesufficient for anti-theft uses, since they typically need to be within ashort distance of the reader to obtain sufficient power to operate. Itwould be useful and/or desirable if a single tag could have bothsufficient circuitry on-board for inventory control and/or “smart card”operations (e.g., auto toll tags, employee identification/securitycards, etc.), while also having an EAS circuit with an operational rangesufficient for compatibility with present EAS systems.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to dual use or multi-mode(e.g., EAS and RFID) identification tags and methods for making andusing the same. The multi-mode identification tag generally comprises anantenna, an electronic article surveillance (EAS) function block coupledto the antenna, and one or more RFID function blocks coupled to theantenna in, thus enabling operation of the tag in both EAS and RFIDmodes. The invention may further relate to systems adapted to usemulti-mode tags embodying one or more of the inventive conceptsdisclosed herein.

In various embodiments, the multi-mode tag comprises a rectifier coupledto the antenna in parallel with the EAS function block, and optionally,with the RFID block as a whole. Alternatively, when the multi-mode tagcomprises multiple RFID function blocks, the rectifier may be coupled tothe antenna in series with at least two of the RFID function blocks. Therectifier generally receives a signal having a characteristic frequency(e.g., a characteristic radio frequency) from the antenna and providesupper and lower power supplies to the RFID function block(s).

In certain embodiments, the rectifier comprises a first path comprisinga first diode coupled between a first AC signal from the antenna and afirst power supply output to the RFID function block(s), and a secondpath comprising a second diode coupled between a second AC signal fromthe antenna complementary to the first AC signal and the first powersupply. In further embodiments, the rectifier further comprises a thirdpath comprising a third diode coupled between a second power supplyoutput to the RFID function block(s) complementary to the first powersupply and the first AC signal, and a fourth path comprising a fourthdiode coupled between the second power supply and the second AC signal.In certain preferred arrangements, each of the first and second paths(and when present, each of the third and fourth paths) comprises a pairof diodes in series.

In certain embodiments, the rectifier includes a resonating circuit witha load effective to reduce the Q of the tag. In various implementations,the resonating circuit may include a programmable threshold device or adevice having a turn-on threshold sufficiently high to delay atransition from the high-Q state to the low-Q state, thereby preventingthe tag from transitioning into the low-Q state at a low voltage. Forexample, the turn-on threshold of the high turn-on threshold device maybe above an EAS read threshold, thereby enabling the tag from beingdetectable as an EAS tag. In either the programmable or high turn-onthreshold case, the device generally comprises a transistor.

The programmable threshold device may comprise a transistor programmedto have a threshold sufficiently low to maintain the tag in a low Qstate until the tag is removed from an electric field. In otherembodiments, the programmable threshold device may have a size suchthat, in a high power electric field, the rectifier supplies sufficientpower for the tag to communicate with the reader. Alternatively oradditionally, the multi-mode tag may comprise logic configured to changethe threshold of the programmable threshold device to a relatively highvalue so that the antenna enters a high Q state (e.g., to turn on theEAS).

In other embodiments, the multi-mode identification tag has (i) a high Qstate in an electric field having a relatively low power and (ii) a lowQ state in an electric field having a relatively high power. Forexample, the antenna may comprise a nonlinear magnetic material having arelatively low loading in an electric field having a relatively lowpower and a relatively high loading in an electric field having arelatively high power, the relatively high and low loadings beingeffective to provide the tag with the high Q state at the relatively lowpower and the low Q state at the relatively high power. In anotheraspect, the tag has the high Q state when the power of the electricfield is below a first threshold and the low Q state when the power ofthe electric field is above a second threshold, the second thresholdbeing greater than or equal to the first threshold.

In one implementation, the rectifier is substantially non-operational ordisabled when the tag has the high Q state, but is operational orenabled when the tag has the low Q state. In another implementation, theRFID function block(s) are substantially non-operational, disabled orelectrically disconnected from a power supply when the tag has the highQ state, and the RFID function block(s) are substantially operational,enabled or electrically connected to the power supply when the tag hasthe low Q state. Optionally, when the tag is in an electric field havinga power above a first predetermined threshold, a sufficient number ofthe RFID function block(s) are enabled or electrically connected to thepower supply to lower the Q of the tag to the low Q state. Alternativelyor additionally, when the power of the electric field is below a secondpredetermined threshold, a sufficient number of the RFID functionblock(s) are disabled or electrically disconnected from the power supplyto maintain the Q of the tag in the high Q state. In this latter case,the second predetermined threshold is less than or equal to the firstpredetermined threshold.

The RFID function block(s) in the present multi-mode identification tagmay comprise a demodulator or clock extractor configured to receive asignal from the antenna and provide a clock signal to remaining RFIDfunction block(s) in response thereto; logic configured to receive theclock signal from the demodulator or clock extractor and provide anidentification signal in response thereto; and/or a modulator or outputstage configured to transmit the identification signal or a modulatedidentification signal to the antenna. The logic may comprise a memorystoring a bit string, and the identification signal may comprise the bitstring. In a further embodiment, the logic may be configured to silencethe tag for a period of time and re-transmit the bit string thereafter.

The EAS function block in the present multi-mode identification tag maycomprise a capacitor. In general, the capacitor has a predeterminedbreakdown voltage. Furthermore, the antenna in the present multi-modeidentification tag may comprise a coil (similar to conventional EASand/or RFID tags) and a tuning element. The tuning element may comprisea second coil, a capacitor or capacitor plate, or a tuning ring.

The method of reading an identification tag generally comprises applyingan electric field to the tag, detecting the tag when the electric fieldhas a relatively low power, and detecting an identification signal fromthe tag when the electric field has a relatively high power. In thepresent method, the electric field is typically generated by a tagreader. Thus, the present method may further comprise generating a pulsefrom the reader to increase the power of the electric field over aperiod of time sufficiently short to maintain a legal or compliantaverage power (i.e., below national and/or international standards forelectromagnetic interference [EMI]). In addition, the pulse should havea length sufficient for the reader to sense the tag if it is present inthe electric field.

In one embodiment of the method, as for the tag itself, the tag includesan tag having a high Q state when the power of the electric field isbelow a first threshold and a low Q state when the power of the electricfield is above a second threshold, the second threshold being greaterthan or equal to the first threshold. Accordingly, in the presentmethod, the tag may comprise a rectifier that is substantiallynon-operational or disabled when the tag has the high Q state, and therectifier is operational or enabled when the tag has the low Q state.Alternatively or additionally, the tag may comprise one or more RFIDfunction block(s) that are substantially non-operational, disabled orelectrically disconnected from a power supply when the tag has the highQ state, and the RFID function block(s) are substantially operational,enabled or electrically connected to the power supply when the tag hasthe low Q state.

In certain embodiments, when the power of the electric field is above afirst predetermined threshold, a sufficient number of the RFID functionblock(s) are enabled or electrically connected to the power supply tolower the Q of the tag to the low Q state. Alternatively oradditionally, when the power of the electric field is below a secondpredetermined threshold, a sufficient number of the RFID functionblock(s) are disabled or electrically disconnected from the power supplyto maintain the Q of the tag in the high Q state, the secondpredetermined threshold being less than or equal to the firstpredetermined threshold.

The present invention advantageously provides a tag that provides bothan EAS function and a RFID function. Thus, the tag is useful as an RFIDtag, both before and after the EAS function is disabled. As a result,manufacturers, wholesalers, distributors and retailers can use a singletag for RF and EAS functions, thereby simplifying product and inventorymanagement and potentially reducing the costs of performing and/orproviding both functions.

These and other advantages of the present invention will become readilyapparent from the detailed description of preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a first embodiment of the presentmulti-mode identification tag.

FIG. 2 is a block diagram showing a second embodiment of the presentmulti-mode identification tag, including a rectifier.

FIG. 3A is a block diagram showing a third embodiment of the presentmulti-mode identification tag, configured for a counter-basedidentification process.

FIG. 3B is a block diagram showing a fourth embodiment of the presentmulti-mode identification tag, configured for a shift register-basedidentification process.

FIG. 4 is a circuit diagram of an exemplary EAS block and rectifierparticularly useful in the present multi-mode identification tag.

FIG. 5 is a flow diagram of an exemplary process for reading the presentmulti-mode identification tag, in accordance with the present invention.

FIG. 6 is a flow diagram of another exemplary process for using thepresent multi-mode identification tag, in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentinvention.

Some portions of the detailed descriptions that follow are presented interms of processes, procedures, logic blocks, functional blocks,processing, and other symbolic representations of operations on code,data bits, data streams or waveforms within a computer, processor,controller and/or memory. These descriptions and representations aregenerally used by those skilled in the data processing arts toeffectively convey the substance of their work to others skilled in theart. A process, procedure, logic block, function, process, etc., isherein, and is generally, considered to be a self-consistent sequence ofsteps or instructions (or circuitry configured to perform or execute thesame) leading to a desired and/or expected result. The steps generallyinclude physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical, magnetic,optical, or quantum signals capable of being stored, transferred,combined, compared, and otherwise manipulated in a computer or dataprocessing system. It has proven convenient at times, principally forreasons of common usage, to refer to these signals as bits, waves,waveforms, streams, values, elements, symbols, characters, terms,numbers, or the like, and to their representations in computer programsor software as code (which may be object code, source code or binarycode).

It should be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities and/or signals,and are merely convenient labels applied to these quantities and/orsignals. Unless specifically stated otherwise and/or as is apparent fromthe following discussions, throughout the present application,discussions utilizing terms such as “processing,” “operating,”“computing,” “calculating,” “determining,” “manipulating,”“transforming” or the like, refer to the action and processes of acomputer or data processing system, or similar processing device (e.g.,an electrical, optical, or quantum computing or processing device orcircuit), that manipulates and transforms data represented as physical(e.g., electronic) quantities. The terms refer to actions and processesof the processing devices that manipulate or transform physicalquantities within the component(s) of a circuit, system or architecture(e.g., registers, memories, other such information storage, transmissionor display devices, etc.) into other data similarly represented asphysical quantities within other components of the same or a differentsystem or architecture.

Furthermore, in the context of this application, the terms “wire,”“wiring,” “line,” “signal,” “conductor” and “bus” refer to any knownstructure, construction, arrangement, technique, method and/or processfor physically transferring a signal from one point in a circuit toanother. Also, unless indicated otherwise from the context of its useherein, the terms “known,” “fixed,” “given,” “certain” and“predetermined” generally refer to a value, quantity, parameter,constraint, condition, state, process, procedure, method, practice, orcombination thereof that is, in theory, variable, but is typically setin advance and not varied thereafter when in use.

Similarly, for convenience and simplicity, the terms “clock,” “time,”“timing,” “rate,” “period” and “frequency” are, in general,interchangeable and may be used interchangeably herein, but aregenerally given their art-recognized meanings. Also, for convenience andsimplicity, the terms “data,” “data stream,” “bits,” “bit string,”“waveform” and “information” may be used interchangeably, as may theterms “connected to,” “coupled with,” “coupled to,” and “incommunication with” (which may refer to direct or indirect connections,couplings, or communications), but these terms are generally given theirart-recognized meanings herein. Further, a “tag” may refer to a singledevice or to a sheet and/or a spool comprising a plurality of attachedstructures, suitable for electronic article surveillance (EAS), highfrequency (HF), ultrahigh frequency (UHF), radio frequency (RF) and/orRF identification (RFID) purposes and/or applications.

Embodiments of the present invention advantageously provide anidentification tag that has both EAS and RFID functions. Thus, the tagis useful as an RFID tag, before (and optionally, after) the EASfunction is disabled. As a result, manufacturers, wholesalers,distributors and retailers can use a single tag for RF and EASfunctions, thereby simplifying product and inventory management andpotentially reducing the costs of performing and/or providing bothfunctions. However, in some embodiments, both RFID and EAS functions canbe disabled by simply deactivating the EAS block.

The invention, in its various aspects, will be explained in greaterdetail below with regard to exemplary embodiments.

An Exemplary Multi-Mode Identification Tag

In one aspect, the present invention concerns a multi-modeidentification tag. The tag generally comprises an antenna, anelectronic article surveillance (EAS) function block coupled to theantenna, and one or more RFID function blocks coupled to the antenna inparallel with the EAS function block. Thus, in one respect, theinvention relates to a combination RFID/EAS product which incorporatesRFID functionality while retaining interoperability with EAS anti-theftsystems. The dual mode RFID/EAS tag uses the basic functionality of anRFID chip, but may operate the tag at 8.2 MHz, rather than at 13.56 MHz.On-chip capacitance may provide the LC tuning necessary for resonance at8.2 MHz. As a result, the present dual mode RFID/EAS tag does notrequire a separate external capacitor or coil.

FIG. 1 shows a first exemplary embodiment of a suitable dual-mode tagarchitecture 100. The architecture 100 includes an antenna 110, an EASfunction block 120, and an RFID portion 170 (e.g., as described in U.S.patent application Ser. Nos. 11/544,366 and 11/595,839, filed on Oct. 6,2006 and Nov. 8, 2006, respectively, the relevant portions of which areincorporated herein by reference). The EAS function block 120 is coupledto the antenna 110 in parallel with part or all of the RFID block 170(e.g., RF→DC rectifier block 180, logic 150, and modulator 140, whichmay be in series as shown in FIG. 1). /In one embodiment, the EASfunction block may comprise a linear and/or non-linear capacitor, asdescribed in U.S. Pat. No. 7,152,804 and/or U.S. patent application Ser.No. 11/104,375, filed Apr. 11, 2005, the relevant portions of which areincorporated herein by reference. Each of the functional blocks in FIG.1 is largely known in the art, and unless otherwise described or claimedherein, is as known in the art.

In further embodiments, RFID block 170 may further comprise ademodulator/clock generator block 130 (e.g., in parallel with therectifier 180) and/or memory 160 (which may contain programming and/orconfiguration information for logic and/or I/O control block 150). Inalternative embodiments, RF→DC rectifier block 180 can be substituted bya very high frequency (VHF)→DC rectifier block or an ultrahigh frequency(UHF)→DC rectifier block (see, e.g., U.S. patent application Ser. Nos.11/595,839 and 11/544,366, the relevant portions of which areincorporated herein by reference).

The dual use tag 100 (e.g., having properties and/or characteristicssufficient for use in both EAS and RFID applications) may be designed tohave a high Q when the applied power is low and the rectifier is notfunctional. The high Q (e.g., a property of the antenna 110) providesdetection ranges of several feet or more and thereby allows thecorresponding EAS reader to sense that there is a tag in its field, butthe reader will generally not have enough power to turn on the tag tosend data. The Q of the tag may then decrease when the power is high,because the extra load of the rectifier 180 may increase the losses inthe system and thereby lower the Q. Thus, the dual use tag 100 may havea high Q and a substantially non-operational or disabled rectifier 180in an applied field below a particular power threshold, and a low Q andan operational or enabled rectifier 180 in an applied field above thethreshold. The threshold may be selected such that, for example, the EASfunctionality operates at a range of up to several feet (e.g. at leastone foot and preferably up to 4 or 5 feet), while the RFID functionalitymay operate at a range of at most about one foot.

Reducing the Q of the tag's inductor may be achieved by using nonlinearmagnetic materials in the antenna 110 that show enhanced loading athigher incident powers, such that losses generally increase withincreasing power. This approach effectively lowers the Q of the tag at ahigh power, such as is generally used in RFID mode, relative to the Q ata low power, such as is generally used in EAS mode. An alternate methodof altering the Q of the tag makes use of switching on portions of theRFID tag circuitry 170 (e.g., rectifier 180, demodulator/clock 130,etc.) at high incident RF powers to increase the current draw of thecircuit, hence degrading the Q of the tag. These circuits could bedesigned to stay off at low incident powers, thus ensuring a high-Qduring EAS mode operation of the tag.

The high Q state allows the tag to be read from a distance large enoughfor the tag to be useful as an EAS device. The applied power in such acase may be moderately high compared to the available maximum set by theFCC, but signal pulsing may be used by the reader to increase the powerover a proportionately short time, while maintaining a legal orcompliant average power. Since the tag is generally not powering up inthe high Q state or EAS mode (e.g., the rectifier is not operational),the pulse can be short, just long enough to sense if there is a tagpresent. Also, in the EAS mode, the tag is usually a relatively longdistance away from the reader (e.g., >1 foot), so that even though thereader power may be relatively high, the power the tag sees is low so itstays in the high Q mode and is not disabled by the reader, even ifsignal pulsing is not used. In contrast, the low Q state may be usedwithin a few centimeters of a reader (e.g., <5 cm), as is typical of thecheckout counter environment (e.g., the RFID mode). The low Q in theRFID mode may not matter (e.g., for signal reception purposes) becausethe power available is relatively high due to the short distance to thereader, although at sufficiently short distances, a low Q may bedesirable (e.g., so as not to exceed the breakdown voltage of devices onthe tag, e.g., in the rectifier). The power in the RFID mode can also bepulsed, but in such an embodiment, the pulse length is generally longerthan in the EAS mode, so that the chip powers up and sends its databefore the power decreases to a level disabling the rectifier. Thereaders in checkout counter applications (e.g., using the RFID mode ofthe tag) and the readers in retail/security applications (e.g., at anexit of a building, using the EAS mode of the tag) are generallydifferent due to the different operating modes of the inlay (tag).

Sweeping (or varying) the frequency in both of the EAS and RFID modesmay be desirable, since doing so dramatically reduces the manufacturingtolerance requirements for the tag. Thus, a single multi-mode tag design(e.g., the tag of FIG. 2) may be used at any frequency within the rangeof the characteristics of the transistors on the tag, and in EAS mode,the present tag may be detected by sweeping the frequency of a readerand monitoring the current flowing through the reader coil to detect adip indicative of resonant loading of the reader by the tag.Additionally, a single multi-mode tag design may be used at anyfrequency within the range of the characteristics of the transistors onthe tag. An RFID tag (along with the corresponding reader) may bedesigned to function at 13.56 MHz, as well as other frequencies. Thus,as explained herein, an exemplary RFID tag designed to function at 13.56MHz can be tuned or modified to function at 8 MHz.

However, in practice, such tags generally operate at frequencies below50 MHz, due to certain technological limits. The reader should bedesigned for a chosen or predetermined frequency (e.g., 13.56 MHz), andthe tag may include a divider (e.g., in demodulator/clock function block130 in FIG. 1) to generate an internal (e.g., on-tag) clock signal.Thus, in one embodiment, a chip designed to provide a 106 KHz clock at13 MHz applied power can provide a ˜65 KHz clock at 8 MHz applied power.

The present tag is not limited, however, to divided clock architectures.For example, at UHF frequencies, the clock may be a modulated signal onthe UHF carrier, and may thus be demodulated to obtain the necessaryclock signal for the tag (see, e.g., the tag architecture of FIG. 1,which may also be suitable for HF frequencies, depending on the designof the antenna; see e.g., U.S. patent application Ser. Nos. 11/544,366and 11/595,839, filed on Oct. 6, 2006 and Nov. 8, 2006, respectively).For example, a 200 kHz clock could be modulated onto a 900 MHz carriersignal. The use of a modulated clock would allow the carrier frequencyto be changed while keeping the data rate fixed (provided the modulatedsignal stayed unchanged).

In an alternate embodiment, the clock signal (e.g., the output ofdemodulator/clock function block 130) could be generated on-chip using alocal oscillator, as part of demodulator/clock function block 130 or (atleast in part) external to block 130, such as in a crystal oscillator.Such an approach may make the data rate entirely independent of thecarrier frequency. Typically, however, such an architecture may be moreprone to clock frequency drift. A reader capable of dealing with suchdrift may take advantage of such an architecture. For example, for a13.56 MHz carrier, a local oscillator on the tag may generate an 800 kHzclock signal and use this clock frequency for communication purposes.

A mechanism for preserving a high Q in a combination RFID/EAS tag wherethe EAS mode functions at long ranges (e.g., >10 cm) and the RFID modefunctions at short ranges (e.g., <5 cm, where the available power islarger) may include a rectifier on the dual-mode RFID chip which has amoderately high threshold of operational voltage. Thus, in such anembodiment, the dual-mode chip does not draw any significant power aslong as the AC voltage on the coil is small (e.g., below a certain orpredetermined threshold), thereby preserving the high Q for EASoperation. When the AC voltage on the coil exceeds the threshold (whichmay be selectable, programmable, tunable, etc.), the chip rectifierturns on, reducing the Q of the multi-mode tag while supplying power torun the RFID mode of the chip. This may be implemented by using a diodechain to control the turn-on threshold of the diode-wired transistors inthe rectifier (see, e.g., U.S. Provisional Patent Application No.60/749,121, filed Dec. 7, 2005, and U.S. patent application Ser. No.11/521,924, filed Sep. 15, 2006, the relevant portions of which areincorporated herein by reference). Such a design generally uses a diodechain circuit similar to a voltage-controlled shunt.

Extra load in the resonating circuit on the coil side of the rectifier(e.g., 410) generally reduces the Q of the antenna 410. Reduced Qgenerally means that the tag cannot be easily detected by the EASreader. However, the tag can still be read by the RFID reader because ofthe high available power. Advantageously, a programmable thresholddevice may be placed in a resonating circuit in the rectifier. In thehigh power operating mode, logic (e.g., logic block 150 in FIG. 1) mayprogram the threshold of a transistor in the rectifier such that itwould stay at a low threshold after power is removed. This leaves thetag in a low Q (or unreadable) state for the EAS reader. However, theprogrammable threshold device in the rectifier can be sized such thatthe high power of the RFID reader could still supply enough power tocommunicate with the tag. During this latter type of communication, thelogic can be configured to change the threshold to a high value so thatthe Q is high and the EAS reader can read the tag. In this way, the EASfunction can be turned on and off as needed or desired.

An additional variation may include tuning the tag such that when therectifier is not powered up or operational, the operating frequency maybe one value, but then when the tag (or rectifier) powers up, an on-tagcapacitance may change to allow it to operate efficiently at a differentfrequency (see, e.g., U.S. Provisional Patent Application No.60/592,596, filed Jul. 31, 2004, and U.S. patent application Ser. No.11/104,375, filed Apr. 11, 2005, the relevant portions of which areincorporated herein by reference).

In an alternative embodiment, detection in EAS mode may be achieved byusing the reader to send two separate signals at different frequencies,and exploiting the nonlinearity of the tag to mix the two signals.Detection could be achieved by monitoring for the presence of sidebandson the higher frequency signal sent by the reader (see, e.g., U.S.patent application Ser. No. 11/104,375, filed Apr. 11, 2005, therelevant portions of which are incorporated herein by reference). Forexample, the reader can send signals at 900 MHz and 100 kHz, and in thepresence of a tag, sidebands would be created at 900.1 MHz and 899.9MHz. In the absence of a tag, no such sidebands exist.

A mechanism for preserving a high Q in a combination RFID/EAS tag wherethe EAS mode functions at long ranges (e.g., >10 cm) and the RFID modefunctions at short ranges (e.g., <5 cm) where the available power islarger, may include a rectifier (see, e.g., the rectifier 425 in theexemplary EAS circuit 400 of FIG. 4) on the dual-mode RFID chip. Therectifier may have a moderately high threshold of operational voltage.Thus, in such an embodiment, the dual-mode chip does not drawsignificant power as long as the AC voltage on the coil is small (e.g.,below a certain or predetermined threshold), thereby preserving the highQ for EAS operation. When the AC voltage on the coil exceeds thethreshold (which may be selectable, programmable, tunable, etc.), thechip rectifier turns on, reducing the Q of the combination tag whilesupplying power to run the RFID mode of the chip. This may beimplemented using a diode chain 420 (e.g., series-connected diodes 422and 424) to control the turn-on threshold of diode-wired transistors inthe rectifier 400 (see, e.g., U.S. Provisional Patent Application No.60/749,121, filed Dec. 7, 2005, and U.S. patent application Ser. No.11/521,924, filed Sep. 15, 2006, the relevant portions of which areincorporated herein by reference). Such a design uses the diode chaincircuit (e.g., series-linked diode chain 420) similarly to avoltage-controlled shunt. Alternatively, the diode-wired transistors(e.g., 422 and 424) may be replaced with true diodes (e.g., Schottkydiodes, as disclosed in U.S. Pat. No. 7,152,804, the relevant portionsof which are incorporated herein by reference) to reduce the circuitsize or to allow the rectifier (and therefore the high-Q/low-Qswitching) to operate at higher frequencies (UHF, for example). Infurther embodiments, one may include more than 2 transistors or diodes(especially if they are Schottky-type diodes rather than diode-wiredtransistors) in series to control the turn-on threshold of the rectifier400.

An additional variation may include tuning the tag such that when therectifier is not powered up or operational, the operating frequency maybe one value, but then when the tag (or rectifier) powers up, an on-tagcapacitance may change to allow it to operate efficiently at a differentfrequency (see, e.g., U.S. Provisional Patent Application No.60/592,596, filed Jul. 31, 2004, and U.S. patent application Ser. No.11/104,375, filed Apr. 11, 2005, the relevant portions of which areincorporated herein by reference).

Permanently disabling the tag may be accomplished by supplying a veryhigh energy pulse in the RFID reader, such that a device in thetuning/rectifier region of the chip (e.g., one of series capacitors 442or 444) is severely damaged. Alternatively, if a programmable thresholddevice having a very low, or even negative, threshold voltage isemployed, the EAS tag becomes undetectable (due to the low Q produced bythe normally on device) until the programmable threshold device isprogrammed into a higher threshold voltage state. Thus, a disabled tag(e.g., programmed into a low threshold voltage state) would not normallycome back to life over time.

As is taught in U.S. patent application Ser. No. 11/104,375, therelevant portions of which are incorporated herein by reference), twoantennae in close proximity can cause either or both of the antennae toact differently than they would independently. Two different antenna onthe same inlay (or tag) can be configured or tuned such that eachantenna acts as designed to for an intended function (e.g., one antennafor EAS operation[s], a second for RFID operation[s]). In oneembodiment, an 8 MHz antenna/fixed capacitor combination may provide theEAS function on the same tag as a 13 MHz antenna connected to the logiccircuitry. HF and UHF antennae can also be similarly combined.

Exemplary Methods of Using the Present Multi-Mode Tag

A further aspect of the present invention concerns a method of readingthe multi-mode identification tag. For example, the method of readingthe tag generally comprises applying an electric field to the tag,detecting the tag when the electric field has a relatively low power,and detecting an identification signal from the tag when the electricfield has a relatively high power. In the present method, the electricfield is typically generated by a tag reader.

FIG. 5 shows one exemplary embodiment 500 for using the presentmulti-mode tag. The tag may be used for EAS (e.g., anti-theft)operations in one mode, for example, and in identification operations(e.g., RF, HF, VHF or UHF) in another mode. In a preliminary step 504,the identification portion of the tag (e.g., memory 160 in FIG. 1) maybe programmed with identification information (e.g., a bit string, whichmay be unique per se or unique within a predetermined sample orpopulation size). If the tag is in an electromagnetic (EM) field ofsufficient strength to activate part or all of the circuitry on the tag(step 506), then the tag will enter one of two modes, depending on acharacteristic of the tag or of the EM field. Otherwise, the processends (512).

In the example of FIG. 5, if the EM field has a relatively high power(e.g., above a first power threshold), then the tag operates in theidentification mode. The high power of the EM field causes the Q of theantenna or the tag to have a relatively low value (e.g., below a first Qthreshold), but activates the RFID logic circuitry. The tag may transmitthe identification information (e.g., a bit string) to the reader instep 508, then in a preferred embodiment, remain silent for apredetermined period of time (using a so-called tags-talk-first, or“TTF,” protocol) in step 510. If the information is read by the tagreader, then the tag (or article having the tag affixed thereto) can beremoved from the EM field until the tag is reused later.

On the other hand, If the EM field has a relatively low power (e.g.,below a second power threshold, which can be the same as or less thanthe first threshold), then the tag operates in an EAS mode. First, if areturn signal is not detected by the reader in step 516, then the EASportion of the tag has probably been deactivated, and the process canend (518). However, if the reader detects a return signal from the tagin EAS mode, the EAS block of the tag can be deactivated (step 522) onthe condition that the tag is within the deactivation range of adeactivation pad associated with the reader (block 520). Thereafter, thetag can still be deactivated if it is moved closer to the pad (see step524); otherwise, the EAS portion can be used again when the tag (orarticle having the tag affixed thereto) is moved back into an EM fieldhaving sufficient power to cause the tag to return an EAS oridentification signal.

FIG. 6 shows another exemplary embodiment 600 for using the presentmulti-mode tag. Like in FIG. 5, identification information may beprogrammed into the memory (e.g., 160 in FIG. 1) of a multi-mode tag instep 604. If the tag is in an electromagnetic (EM) field of sufficientstrength to activate part or all of the RFID circuitry on the tag, thenthe identification information on the tag can be read in step 606 (FIG.6). If not, an indicator or flag can be set (e.g., in the reader) towait a predetermined period of time until a characteristic EAS delayexpires (step 608).

In the example of FIG. 6, if the reader reads the identificationinformation on the tag, the reader then attempts to validate theidentification information using a database of valid identificationinformation in step 610. In a preferred embodiment, if the data cannotbe validated, a flag or indicator indicating that the data may beinvalid (such as a light of a particular color [e.g., yellow] or anauditory alarm such as a siren) is set in the reader in step 612. If theinformation is read and validated by the tag reader, then the tag (orarticle having the tag affixed thereto) can be removed from the EM fielduntil the tag is reused later, or the EAS portion (e.g., block 120 inFIG. 1) of the tag can be deactivated (e.g., if the article is beingpurchased or checked out and removed from the secure location in whichit was kept, such as a warehouse, retail store, or library).

Like in the example of FIG. 5, if the reader determines that the tag isnot within an EAS deactivation range (e.g., a return EAS signal is notdetected), in step 522, the reader may activate a flag or indicator thatindicates to the user that the tag is not close enough for deactivation.Thereafter, the tag can still be deactivated if it is moved closer tothe pad (see step 520). However, if the reader determines that the tagis within the deactivation range (e.g., a return EAS signal isdetected), in step 530, an EM field having sufficient power todeactivate the tag (and/or the EAS portion thereon) is applied. Thereader then confirms deactivation by attempting to read theidentification information on the tag in step 640. If the identificationdata is read, an indicator (such as a light of a particular color [e.g.,red], or an auditory alarm such as a buzzer) indicating thatdeactivation failed may be triggered or turned on. If the identificationdata is not read, an indicator (such as a light of a particular color[e.g., green], or an auditory alarm such as a bell) indicatingsuccessful deactivation may be triggered or turned on.

The following description explains the operations of a combinationRFID/EAS tag that operates in conformance with existing 8.2 MHz EASsystems. The operations fall into two broad categories: operation of theRFID function prior to or at checkout, and EAS deactivation (e.g., atcheckout in retail applications) and detection at the sensor.

Exemplary RFID Operations

RFID operations at 8.2 MHz are possible using the multi-mode tag 100.One exemplary RFID block 270 can include or be based on an RFID devicehaving a predetermined number of bits (e.g., 2 or more bits, such asfrom m*2^(n), where m and n are independently integers of at least 1,and at least one of m and n is at least 2; in one embodiment, m*2^(n) is96 bits) in memory 160 and that may be capable of operating in the 13.56MHz frequency band. In a preferred embodiment, memory 160 comprises aROM (e.g., fuse bank, mask-programmable ROM, or EPROM). In some of theseembodiments, the functional operation of the RFID block or portion 170of the tag at 13.56 MHz can be used independent of the multi-modeoperations of the device 100.

The exemplary tag 100 may transmit a ((m*2^(n))/p)-bit code, where p isan integer of 1 or more (in one embodiment, 1), on absorbing sufficientpower as it enters the reader's 13.56 MHz RF field. A simple TTF (tagstalk first) anti-collision scheme can be implemented thereon, whichallows several tags in the reader's field to be differentiated (see,e.g., U.S. Provisional Patent Application No. 60/748,973, filed Dec. 7,2005, and U.S. patent application Ser. No. 11/544,366, filed Oct. 6,2006, the relevant portions of which are incorporated herein byreference, for an example of such a scheme.

However, rather than attempt to run the RFID at 13.56 MHz and the EAS at8.2 MHz, the RFID portion may be run at the same frequency as the EASportion of the tag. The strategy removes the need for separately tuningthe RFID and EAS portions of a combination RFID/EAS tag. The reader insuch an application is generally configured to read the combinedRFID/EAS tag operating at 8.2 MHz.

Although RFID tags are generally designed to operate at 13.56 MHz, theRFID portion 170 of the dual mode tag 100 can be operated at 8.2 MHzsimply by retuning the resonant frequency (see, e.g., U.S. patentapplication Ser. No. 11/104,375, filed Apr. 11, 2005, the relevantportions of which are incorporated herein by reference). Retuning canalso be done by changing the antenna inductance and/or the on-chiptuning capacitor value, as disclosed in U.S. patent application Ser. No.11/104,375.

The exemplary RFID block 170 transmits its data (or code) using a subsetof the ISO 14443 Type A air interface specification. The data istransmitted on the 847 KHz sideband at a rate of 106 kbps, usingManchester encoding. Thus, in one embodiment, transmission of 96 bitstakes approximately 0.9 milliseconds. The same transmission protocol canbe used at 8.2 MHz, with appropriate scaling of the sub-carrierfrequency and data rate.

Power Availability at 8.2 MHz

The Federal Communications Commission (FCC) limits the magnetic fieldstrength provided by the carrier at 8.2 MHz to only 1% of that at 13.56MHz (i.e., 0.1 mV/m at 30 m for 8.2 MHz, vs. 10 mV/m at 30 m for 13.56MHz). Converting this to a near-field magnetic field, the maximumpermissible field strength at 3 cm would be about 10 A/m at 8.2 MHz, but365 A/m at 13.56 MHz. However, by pulsing the 8.2 MHz carrier at a 10×peak power and a 10% duty cycle, short bursts (e.g., a maximum pulselength of about 12 nsec or less) can reach 100 A/m. Equivalent pulselengths and power increases can be easily determined by one skilled inthe art, in accordance with design and/or application choices.

At 13.56 MHz, the exemplary tag 100 can operate in the RFID made at arange of up to 4 cm from a conventional reader, requiring a magneticfield of approximately 15 A/m to power the RFID block 170 of the tag100. While this requirement exceeds the average power of 10 A/mavailable at 8.2 MHz, it falls well within the power available from apulsed power source operating at a 10× X peak power and 10% duty cycle.In addition, the power consumption of the exemplary tag 100 will belower for 8.2 MHz operation than for 13.56 MHz operation due to thelower dynamic power consumed at the reduced operating frequency.

Exemplary EAS Functionality

Combining the exemplary RFID block 170 with technology compatible withexisting 8.2 MHz EAS systems, without affecting existing EAS systemoperation, presents two hurdles for the present dual-mode tag 100.First, the RFID portion 170 of the RFID/EAS tag 100 must be readable(e.g., at retail checkouts) without interfering with EAS deactivation orcausing inadvertent deactivation. Second, the functionality of RFIDblock 170 should not interfere with EAS detection; i.e., RFIDfunctionality should operate orthogonally to the EAS function(s) 120.

The exemplary RFID tag requires approximately 10, 12, 14 or more voltsAC to be generated on the coil (e.g., across the Coil1/Coil2 terminals)to function correctly. This voltage may be too high for the capacitor ona conventional EAS tag. For example, the capacitor on one exemplary EAStag might undesirably fail or deactivate during a typical read operationof the RFID portion. However, the EAS portion 120 should deactivate whena higher voltage is applied to it. As a result, an “on-chip” capacitor(e.g., integrated with the RFID circuitry 170 on a single substrate) maybe used for both deactivation of the EAS block 120 (e.g., a capacitortherein) and/or for tuning the resonance of tag 100 to another frequency(e.g., 8.2 MHz), removing the need for a separate EAS tag capacitor.Using existing systems (with minor modification[s] as discussed herein),power should be available to rupture (or short-circuit) the on-chipcapacitor in EAS block 120, even though it takes a voltage higher thanthat for operation of the RFID block 170.

Intentional deactivation of the EAS block 120 is relatively facile inthe present scheme. The on-chip capacitor in the EAS block 120 of theexemplary tag 100 can undergo irreversible breakdown upon application ofa voltage of approximately 30-40 volts, for no more than about onemillisecond, to induce tag deactivation. This voltage can readily beachieved on an LC tag in close proximity to an EAS tag deactivation padusing current technology.

Using an LC circuit containing a load resistance representative of apreferred impedance of the exemplary RFID block 170, a potential of 40 Vcan be obtained on the coil at a range of at least 1.5 cm from the EASdeactivation pad. Although this range is shorter than the operatingrange of the RFID block 170 (e.g., about 3-4 cm), the deactivation rangeis close to the RFID range, and further optimization may improve the EASdeactivation range. Alternatively or additionally, altering thedeactivation pulses provided by the deactivation pad may improve thedeactivation range.

EAS tag detection within the desired range requires that the LC circuithave a fairly high Q, in the range of about 60. In a preliminaryexperiment, the exemplary dual-mode tag 100 has been tuned to operate at8.2 MHz, and the Q of the tag was measured. The Q measured for thedual-mode tag 100 is approximately 30% of the Q measured for aconventional EAS tag. Although the Q of the exemplary dual-mode tag 100is lower than what might be desired for optimal operations, improvementsto the exemplary RFID tag have been identified herein that should allowa significant improvement in the dual-mode tag's Q value, making itcompatible with EAS systems.

A Second Exemplary Multi-Mode Tag

FIG. 2 shows a second exemplary embodiment of a dual-mode tagarchitecture 200 suitable for use in the present invention. As for theembodiment of FIG. 1, the dual-mode tag 200 includes an antenna (notshown, but represented by the Coil1/Coil2 terminals), an EAS functionblock 220, a full wave rectifier 202, and an RFID portion 270 (describedin U.S. patent application Ser. Nos. 11/521,924, 11/544,366 and11/595,839, filed on Sep. 15, 2006, Oct. 6, 2006 and Nov. 8, 2006,respectively, the relevant portions of which are incorporated herein byreference). Also similarly to FIG. 1, the EAS function block 220 iscoupled to the antenna (or across terminals thereto) in parallel withRFID portion 270 and/or full wave rectifier 202.

In the embodiment of FIG. 2, an electromagnetic field can be induced onan external coil attached at terminals Coil1 and Coil2 and acrosscapacitor CR. The AC voltage across the coil can be rectified by fullwave rectifier 202 receives the sinusoidal (e.g., alternating orperiodic) signal from the antenna, and provides (i) a DC power supplyacross terminals VDD and VSS and (ii) a supply capacitance, CS.Capacitors CR and CS (which may be on-tag, off-tag, or both [e.g., CS ison-tag and CR is off-tag]) may function to filter the signals to andfrom the antenna and/or to reduce noise on the power supply lines. Inone implementation, the full wave rectifier 202 may be implemented asrectifier 425 of FIG. 4.

Referring back to FIG. 2, the RFID portion may comprise clock extractor204, sequencer 206, memory array 208, data encoder 210, and datamodulator 212. Clock extractor 204 may produce a logic clock forsequencer 206, and memory array 208 can be accessed by signals generatedfrom sequencer 206 to provide a serial data output to data encoder 210.In various embodiments, memory 208 may comprise volatile (e.g., DRAM,SRAM, etc.) or non-volatile memory (e.g., mask ROM, one-timeprogrammable [OTP] ROM such as fuses or EPROM, EEPROM, ferromagnetic RAM[FRAM], etc.), and memory 208 can store a bit string (which can beunique or have one of a predetermined number of values providing asubstantially unique value for a given tag population or sample size)associated with identification information and/or a security orencryption key.

Modulation control can be generated from data encoder 210 and providedto data modulator 212 for output of an RF reply signal to the reader.Thus, the encoder may comprise logic that converts data from the memory208 to signals configured to control the data modulator and/or encodethe data in the RF transmission signal.

The EAS function block 220 generally comprises one or more capacitorshaving a characteristic breakdown voltage. When EAS function block 220comprises more than one capacitor, at least two of the capacitors aretypically (but not necessarily) in series with each other (see, e.g.,capacitor circuit 440 in FIG. 4). The breakdown voltage of the EAScapacitor(s) is generally significantly higher than VDD, usually by 2-3×or more. For example, VDD can be anywhere from about 1.5 V to about 9 V(e.g., 1.8 V, 2.5 V, 3.3 V, 5 V, etc.), but the EAS capacitor breakdownvoltage is generally at least 10 V, and possibly up to 30 or 40 V (e.g.,about 12 V, 15 V, 20 V, 25 V, etc.).

Third and Fourth Exemplary Multi-Mode Tags

FIGS. 3A-3B show exemplary embodiments of dual-mode tag architectures,the RFID portion(s) of which are described in U.S. patent applicationSer. Nos. 11/544,366 and 11/595,839, filed on Oct. 6, 2006 and Nov. 8,2006, respectively, the relevant portions of which are incorporatedherein by reference. These dual-mode architectures further include anEAS function block 320 (FIG. 3A) or 370 (FIG. 3B) coupled to the antenna302 (FIG. 3A) or 352 (FIG. 3B) or across terminals thereto. The EASfunction block 320 or 370 may comprise a linear and/or non-linearcapacitor, as described in U.S. Pat. No. 7,152,804 and/or U.S. patentapplication Ser. No. 11/104,375, filed Apr. 11, 2005, the relevantportions of which are incorporated herein by reference, and functionsimilarly to EAS function block 120/220 above (see also FIGS. 1-2).

In general, an RFID portion of a third embodiment of the dual-mode tag300 can include an antenna section (e.g., 302), a power-up circuit(e.g., 304), a clock subcircuit (e.g., 306), a counter (e.g., 308), amemory portion (e.g., 312), a decoder (e.g., 310), a loop reset circuit(e.g., 314), and an output stage (e.g., 316). Portions of or all suchcircuit portions (except, in some embodiments, the antenna 302) can beprintable in order to reduce overall system costs.

The antenna 302 may be implemented using a resonant LC circuit for useat 13.56 MHz, for example, but tunable for use at, e.g., 8.2 MHz (i.e.,at a frequency typical of EAS applications). Alternatively, the antennamay be implemented using a dipole or similar such antenna for 900 MHz(high frequency, or HF) operation or 2.4 GHz (very high frequency, orVHF) operation. Generally, the antenna may be used to provide power foroperation of the tag circuitry, and to provide information from the tagto the reader or interrogator. Using power-up circuit 304, power can beextracted by rectifying the RF signal collected by antenna 302 andstoring the resultant charge in a storage capacitor (e.g., CS). Thus,when a tag enters a region of space with sufficient electromagneticfield being transmitted from a nearby reader, the capacitor begins tocharge-up, and a voltage across the capacitor increases accordingly.When the voltage reaches a sufficient value, an “enable” signal can begenerated, and this enable signal (e.g., EN) can be used to initiatecircuit operation (e.g., by coupling to clock 306 and counter 308).

In an exemplary clocking subcircuit (e.g., 306), a clock signal can begenerated so as to synchronously operate associated circuitry (e.g.,usually counter 308, but in some embodiments, also memory 312 and/oroutput stage 316). As for other embodiments of the dual-mode tag, thisclock signal may be generated by dividing down the incident RF signalreceived by antenna 302, by generating a local clock signal using anon-chip oscillator, or by demodulating a reader-provided clock signalfrom the received RF signal. This clock signal may be used to drivecounter 308, which may begin counting from a reset state as soon as tagcircuitry 300 is enabled, for example by a reduction in the Q value ofthe antenna 302 or tag 300.

As values of counter 308 increase, a counter output can be used tosequentially select specific bits in memory portion 312. Such a memoryarray may be customized using a maskless process technology (e.g., aprinting process) for 1, 2, or more layers of the tag. In an alternativeembodiment, memory bits forming memory 312 may be made usingconventional photolithographic techniques, and outputs thereof can beconnected using maskless processing (e.g., one or more printing and/orlaser writing/definition processes) to create standard or customized bitsequences.

Bits provided from memory 312 in the dual-mode tag or device 300 may bepassed to output stage 316 for information transfer back to a reader(e.g., in the form of a bit string). The information transfer can beaccomplished by modulation of the tag impedance, for example.Alternatively, other common modulation schemes, such as amplitude shiftkeying and/or frequency shift keying may also be used in accordance withembodiments of the present invention.

In operation, as counter 308 goes through its counting sequence, variousbits or portions of a predefined bit string can be transferred back tothe reader. Simultaneously, loop reset 314 can monitor the state ofcounter 308. After a complete bit string of appropriate length is sentback to the reader, tag 300 can “go silent” and remain in this silentstate until the counter state reaches a specific value. Loop reset 314can then compare the counter value with a value that may be programmedduring tag fabrication using laser fuses or printed OTP memory, forexample. When the counter value and the programmed value are logicallyequal (e.g., each bit of each value matches), loop reset circuit 314 canreset counter 308, and the overall process can be repeated.

FIG. 3B shows an exemplary block schematic diagram 350 including anantenna section (e.g., 352), EAS function block 370, a power-up circuit(e.g., 354), a clock subcircuit (e.g., 356), cyclic shift registers(e.g., 358 and 360), a memory portion (e.g., 362), a delay/reset circuit(e.g., 364), and an output stage (e.g., 366). Portions of or all suchcircuit portions can be printable in order to reduce overall systemcosts. Other than antenna 352 and EAS function block 370, the RFIDfunction block may comprise one or more of the remaining blocks.Preferably, the RFID function block comprises at least power-up circuit354, clock subcircuit 356, a cyclic shift register (e.g., 358 or 360),memory 362, and output stage 366.

The antenna may be implemented similarly to the antenna of otherembodiments. Power-up circuit 354 can rectify the RF signal collected byantenna 352 and store the resultant charge in a storage capacitor. The“enable” signal (e.g., EN) can be generated and used to initiate circuitoperation (e.g., by coupling to clock 356, cyclic shift registers 358and 360, and the delay/reset circuit 364). Clocking subcircuit 356 cangenerate a clock signal so as to synchronously operate associatedcircuitry (e.g., cyclic shift registers 358 and 360, memory 362, and/oroutput stage 366). This clock signal may be generated similarly to otherembodiments described herein. When the clock signal drives cyclic shiftregister 358, a single predetermined state (e.g., a binary “high” bit)may be shifted through all the rows addressing the memory, thusselecting one row of memory at a time. The output of 358 may in turn beused to clock a second cyclic shift register 360, thus shifting a singlehigh bit through all the columns addressing the memory 362, thusselecting a single column of memory at a time. The memory array 362 maybe customized using a maskless process technology (e.g., a printingprocess), as described above, for 1, 2, or more layers of the tag. Theoutput stage 366 may also function similarly to other output stages orsections described herein.

In operation, as cyclic shift registers 358 and 360 go through ashiftable sequence, various bits or portions of a predefined bit stringcan be transferred back to the reader. At the end of the sequence, thedelay/reset circuit 364 can be triggered by the output of 360 to causetag 350 to “go silent” and remain in this silent state for an intervaldetermined by the delay/reset circuit 364. The delay may be apredetermined value, or may be determined based on various environmentalor physical parameters such as temperature, power delivered to the tag,and/or electrical performance of various components within the delaycircuit. When the delay circuit completes its cycle, it can reset shiftregisters 358 and 360, and the overall process can be repeated.

In the embodiments of FIGS. 3A-3B, within a certain/predefined period oftime (e.g., 1 second), a certain number (e.g., X) tags can broadcast andbe read/distinguished by conventional RFID and/or EAS systems and/ortechnology. “X” can be an integer of, e.g., 10, 12, 20, or more devices.Further, additional technological advances, as well as an increasednumber of bits in the bit string, can allow 2^(N) tags or devices to bedistinguished when broadcasting. “N” can be an integer of 5, 8, 10, ormore, for example.

In addition, in the embodiments of FIGS. 3A-3B, one can use a unique tagidentification number as a mechanism for generating corresponding uniquedelays for each tag or device by providing these as inputs to thedelay/reset circuit. Conventional software and/or algorithmic approachescan be used to convert each unique tag identification number into a bitsequence of a different length. For example, bit sequence lengths canrange from 7 to 16, and can result in sufficient differentiation interms of delays between two random tags or devices. Accordingly, any twotags 300/350 under an applied set of detection conditions can bedistinguished due to different bit sequences resulting from unique tagidentification numbers (e.g., values and/or lengths) programmed therein.

An Exemplary EAS Block for Multi-Mode Tags

FIG. 4 shows an exemplary EAS block 400 for use in the presentmulti-mode tags. EAS block 400 may include a rectifier 425 and acapacitor block 440. In one embodiment, capacitor block 440 comprisesseries capacitors 442 and 444, which receive the external signal (e.g.,an 8.2 MHz RF/EAS signal) from antenna 410 and which are configured toprovide the EAS deactivation function. Bridge rectifier 425 may comprisefour series-connected diode pairs (e.g., 420, comprising first diode 422and second diode 424; see, e.g., U.S. patent application Ser. No.11/521,924, filed Sep. 15, 2006, the relevant portions of which areincorporated herein by reference) as shown in FIG. 4. Alternatively, therectifier may comprise a half-wave rectifier (e.g., diode pair 420) or afull-wave rectifier (e.g., two series-connected diode pairs, such asdiode pair 420 and its complement between Vin′ and Vout).Series-connected devices such as diodes 422 and 424 and capacitors 442and 444, and methods of making the same, are described in U.S.Provisional Patent Application No. 60/859,480, filed Nov. 15, 2006, therelevant portions of which are incorporated herein by reference. Load430 across power supply V_(OUT)/V_(OUT′) generally comprises aconventional load resistor.

In FIG. 4, capacitor block 440 may provide the EAS function when it hasan appropriate breakdown voltage (e.g., in the range of ˜10 to 40 V;e.g., from about 10 to about 20 V, from about 20 to about 30 V, fromabout 30 to about 40 V, or any range of values therein; see, e.g., U.S.Pat. No. 7,152,804). Capacitors formed in series may consume about thesame area in the EAS block 400 as a single capacitor having a thickeroxide, but the voltage is divided between two capacitors 442 and 444,instead of having the entire voltage drop across just one capacitor.This makes the capacitor circuit much less “leaky,” and is expected toresult in higher yields in manufacturing. Additionally, one couldadvantageously use the same oxide layer for both the tank capacitors442/444 and the rectifier transistors (e.g., 422 and 424), which mayalso increase the transistor performance by reducing the turn-onvoltage. This embodiment provides process simplicity while optimizingthe performance of both components.

Rectifier 425 may be configured to have one or more of the dual-modecharacteristics and/or provide one or more of the dual-mode functionsdescribed herein. Furthermore, series-connected diodes 422 and 424 maybe configured to divide the voltage equally between the two devices,thereby rendering the peak stress on the gate oxide in the devices 422and 424 similar to the stress on the other logic transistors (e.g., inlogic block 150 in FIG. 1) and possibly increasing rectifier efficiency.The diodes 422 and 424 can be made using the same manufacturing processas the logic transistors, thereby simplifying the manufacturingtechnology and increasing product throughput (e.g., reducing the totaltime of manufacturing).

An Exemplary Method of Making a Multi-Mode Tag

A further aspect of the invention relates to a method of making thepresent multi-mode (e.g., dual-use) tag. Advantageously, the present tagmay be manufactured using printing technology, rather thanphotolithography. Such a manufacturing approach minimizes waste ofmaterials and increases throughput, relative to photolithographicprocesses. Suitable printing processes for forming patterned layers of(doped) silicon, metal, and insulator can be found in U.S. Pat. No.7,152,804 and and U.S. patent application Ser. Nos. 11/243,460,11/104,375, 11/452,108, filed Oct. 3, 2004, Apr. 5, 2005, Jun. 12, 2006,Oct. 6, 2006, respectively, the relevant portions of each of which isincorporated by reference herein.

However, the method is not limited to techniques for printing electronicdevices (e.g., devices with one or more printed layers or structures).The method can also be implemented equally well using fabricationtechniques commonly associated with circuits on single crystalsubstrates (e.g., CMOS circuits on silicon wafers). In one embodiment,for example, load resistors may be placed in the single crystal circuitto provide it with one or more characteristics similar to or the same asthe printed circuit.

One technique that can be used in either case involves configuring therectifier (e.g., 425 in FIG. 4) to have a high threshold voltage and therest of the circuit to have a lower threshold voltage. In such a case,the rectifier turns on only under high power (e.g., in the presence of arelatively high applied electric field, such as that found in closeproximity to a reader). In addition, the operating power to run the restof the logic stays low due to the lower threshold voltages of thetransistors (and other devices) in such logic. In devices on a singlecrystal substrate, this may be done by using different threshold voltageimplants in each of the functional block areas (i.e., the rectifier area202 vs. the RF logic areas 204-212 in FIG. 2). In the case of printeddevices, the threshold of the devices may be varied by adding dopant(s)to the ink(s) such that ink(s) with different doping (or dopant) levelstherein are printed (e.g., by inkjetting or offset lithography) in thedifferent areas. Higher doping typically increases the threshold, andlower doping decreases the threshold.

Working Example

An existing 13 MHz tag, connected to an antenna tuned to 8 MHz, canfunction as an RFID tag close to a reader and as an EAS tag at adistance from the reader, as demonstrated by simulation as well as bymeasurements taken on RFID tag circuitry designed for operation at 13.56MHz, but tested at 8 MHz. A rectifier circuit with a voltage-controlledturn-on has been designed (see, e.g., U.S. patent application Ser. No.11/521,924) and fabricated using Si ink technology (see, e.g., U.S.patent application Ser. Nos. 10/789,317, 10/949,013, 10/950,373, and10/956,714, filed on Feb. 27, 2004, Sep. 24, 2004, Sep. 24, 2004, andOct. 1, 2004 respectively and an externally attached capacitor. Therectifier circuit is configured to prevent the RFID circuitry fromaffecting the EAS operation at a distance. The 8.2 MHz EAS mode antennaresonated strongly enough to be detected by a commercially available EASreader (from Checkpoint Systems), and it also showed that bits in aprogrammed memory are clocked out when the tag is in a higher fieldregion (e.g., representative of or simulating an RFID field). The RFIDcircuitry did not affect the EAS operation at a distance.

In an alternative and/or complementary approach, simulations have shownthat existing 13 MHz RFID tags, connected to an antenna tuned to 8 MHz,can function as an RFID tag close to a reader and as an EAS tag at afarther distance from the reader.

The calculations and experimental data summarized herein demonstrate thedesign and production of a combination (dual mode) RFID/EAS tag,compatible with existing EAS and RFID systems, from existing RFID andEAS devices and technology. Further moderate alterations andimprovements to existing technology may lead to commercially viable dualmode systems. In particular, modifying an exemplary RFID tag to operateat 8.2 MHz, and using the RFID on-chip tuning capacitor to provide EASfunctionality, allows interoperations with existing sensors/readers. TheEAS deactivation range in such a system corresponds to the operatingrange for the RFID portion, which would be several centimeters.

CONCLUSION/SUMMARY

Thus, the present invention provides a multi-mode identification tag andmethods for making and reading the same. The tag generally comprises anantenna, an electronic article surveillance (EAS) function block coupledto the antenna, and one or more RFID function blocks coupled to theantenna in parallel with the EAS function block. The method of readingan identification tag generally comprises applying an electric field tothe tag, detecting the tag when the electric field has a relatively lowpower, and detecting an identification signal from the tag when theelectric field has a relatively high power. In the present method, theelectric field is typically generated by a tag reader. Thus, embodimentsof the present invention advantageously provide the tag with both an EASfunction and a RFID function. Thus, the tag is useful as an RFID tag, atleast before the EAS function is disabled. As a result, manufacturers,wholesalers, distributors and retailers can use a single tag for RF andEAS functions, thereby simplifying product and inventory management andpotentially reducing the costs of performing and/or providing bothfunctions.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

1. A multi-mode identification tag, comprising: a) an antenna; b) anelectronic article surveillance (EAS) function block coupled to theantenna; c) one or more RFID function blocks coupled to the antenna inparallel with the EAS function block; and d) a rectifier configured tobecome (i) substantially disabled in an electric field having an energybelow a first predetermined threshold and (ii) substantially enabledwhen the energy of the electric field is above a second predeterminedthreshold, the second threshold being greater than or equal to the firstthreshold; wherein (i) the tag has a high Q state in the electric fieldhaving an energy below the first predetermined threshold, and (ii) thetag has a low Q state in the electric field having an energy above thesecond predetermined threshold.
 2. The multi-mode identification tag ofclaim 1, wherein the rectifier is coupled to the antenna in parallelwith the EAS function block.
 3. The multi-mode identification tag ofclaim 1, wherein the rectifier is coupled to the antenna in parallelwith the EAS function block, and the rectifier is substantiallynon-operational or disabled when the tag has the high Q state, and therectifier is operational or enabled when the tag has the low Q state. 4.The multi-mode identification tag of claim 1, wherein the RFID functionblock(s) are substantially non-operational, disabled or electricallydisconnected from a power supply when the tag has the high Q state, andthe RFID function block(s) are substantially operational, enabled orelectrically connected to the power supply when the tag has the low Qstate.
 5. The multi-mode identification tag of claim 4, wherein when thetag is in the low Q state, the tag is unreadable and the EAS function isnon-operational.
 6. The multi-mode identification tag of claim 1,wherein when the electric field has a power above the firstpredetermined threshold, a sufficient number of the RFID functionblock(s) are enabled or electrically connected to the power supply tolower the Q of the tag to the low Q state.
 7. The multi-modeidentification tag of claim 6, wherein when the power of the electricfield is below the second predetermined threshold, a sufficient numberof the RFID function block(s) are disabled or electrically disconnectedfrom the power supply to maintain the Q of the tag in the high Q state.8. The multi-mode identification tag of claim 1, wherein the rectifierhas a resonating circuit with a load effective to reduce the Q of thetag.
 9. The multi-mode identification tag of claim 8, wherein theresonating circuit includes a programmable threshold device.
 10. Themulti-mode identification tag of claim 9, wherein the programmablethreshold device comprises a thin film transistor.
 11. The multi-modeidentification tag of claim 10, wherein the thin film transistor has athreshold sufficiently low to maintain the tag in a low Q state untilthe tag is removed from the electric field.
 12. The multi-modeidentification tag of claim 10, wherein the tag includes logicconfigured to change the threshold of the thin film transistor to arelatively high value so that the antenna enters a high Q state.
 13. Themulti-mode identification tag of claim 1, wherein the rectifier receivesa signal having a characteristic frequency from the antenna and providesupper and lower power supplies to the RFID function block(s).
 14. Themulti-mode identification tag of claim 1, wherein the RFID functionblock(s) comprise a demodulator or clock extractor configured to receivea signal from the antenna and provide a clock signal to remaining RFIDfunction block(s) in response thereto.
 15. The multi-mode identificationtag of claim 14, wherein the RFID function block(s) further compriselogic configured to receive the clock signal from the demodulator orclock extractor and provide an identification signal in responsethereto.
 16. The multi-mode identification tag of claim 15, wherein thelogic comprises a memory storing a bit string, and the identificationsignal comprises the bit string.
 17. The multi-mode identification tagof claim 16, wherein the logic is configured to silence the tag for aperiod of time and re-transmit the bit string thereafter.
 18. Themulti-mode identification tag of claim 15, wherein the RFID functionblock(s) further comprise a modulator or output stage configured totransmit the identification signal or a modulated identification signalto the antenna.
 19. The multi-mode identification tag of claim 1,wherein the EAS function block comprises a capacitor.
 20. The multi-modeidentification tag of claim 19, wherein the capacitor has apredetermined breakdown voltage.
 21. The multi-mode identification tagof claim 1, wherein the antenna comprises a coil and a tuning element.22. The multi-mode identification tag of claim 21, wherein the tuningelement comprises a second coil, a capacitor or capacitor plate, or atuning ring.
 23. The multi-mode identification tag of claim 1, whereinthe EAS function block comprises a capacitor.
 24. The multi-modeidentification tag of claim 23, wherein the capacitor has acharacteristic breakdown voltage in the range from about 10 to about 40V.
 25. A method of reading an identification tag, comprising: a)applying an electric field to the tag, wherein (i) the tag has a high Qstate in an electric field having an energy below a first predeterminedthreshold, and (ii) the tag has a low Q state in an electric fieldhaving an energy above a second predetermined threshold, the tag furtherhaving a rectifier configured to become (i) substantially disabled whenthe electric field has an energy below the first predetermined thresholdand (ii) substantially enabled when the energy of the electric field isabove the second predetermined threshold, the second threshold beinggreater than or equal to the first threshold; b) detecting the tag whenthe energy of the electric field is below the first threshold and thetag has the high Q state; and c) detecting an identification signal fromthe tag when the energy of the electric field is above the secondthreshold and the tag has the low Q state.
 26. The method of claim 25,wherein the tag comprises one or more RFID function block(s) that aresubstantially non-operational, disabled or electrically disconnectedfrom a power supply when the tag has the high Q state, and the RFIDfunction block(s) are substantially operational, enabled or electricallyconnected to the power supply when the tag has the low Q state.
 27. Themethod of claim 26, wherein when the energy of the electric field isabove the second predetermined threshold, a sufficient number of theRFID function block(s) are enabled or electrically connected to thepower supply to lower the Q of the tag to the low Q state.
 28. Themethod of claim 27, wherein when the energy of the electric field isbelow the first predetermined threshold, a sufficient number of the RFIDfunction block(s) are disabled or electrically disconnected from thepower supply to maintain the Q of the tag in the high Q state.
 29. Themethod of claim 25, wherein the programmable threshold device comprisesa thin film transistor having a threshold sufficiently low to maintainthe tag in a low Q state until the tag is removed from the electricfield.
 30. The method of claim 29, wherein the tag includes logicconfigured to change the threshold of the thin film transistor to arelatively high value so that the antenna enters a high Q state.